Final answer:
A chromosome is a coiled structure made of DNA and proteins that encode genetic instructions for making proteins. (option 1)
Step-by-step explanation:
A chromosome can be defined as a coiled-up thread of DNA. Chromosomes are long strings of genetic material known as deoxyribonucleic acid (DNA) and are composed of DNA and proteins, including histones. They encode genetic instructions for making proteins. These instructions are organized into units known as genes. Most genes contain the instructions for a single protein, and multiple genes can be found on a single chromosome. Traits, genes, and their variants, called alleles, are all located on chromosomes.
During cell division, chromosomes ensure the DNA is safely transported to the daughter cells. With the help of proteins, DNA coils into the more compact structure of chromatin and eventually forms chromosomes, which stain clearly enough to be seen under a microscope. It is the degree of DNA coiling that determines the structure of a chromosome. An allele, on the other hand, represents a specific version of a gene that influences traits such as hair color or eye color.
Each human cell contains 46 chromosomes, except for the sex cells (sperm and egg), which have 23 chromosomes each. The human genome is thus organized into chromosomes, carrying a vast array of genes that determine everything about an organism from physical traits to disease susceptibility.